Thermal regenerators

ABSTRACT

A microcellular ceramic thermal regenerator disc, for use in a gas turbine engine, has a slot formed in its periphery between adjacent pairs of drive pins, each slot having both its ends terminating short of the two end faces of the disc.

United States Patent 91 Ritchie V Dec. 25, 1973 THERMAL REGENERATORS [76] Inventor: James Alexander Ritchie, 22 Lundy View, Chelmsley Wood, Birmingham, England [22] Filed: Mar. 22, 1972 [21] Appl. No.: 236,946

[52] US. Cl. 165/9, 165/10 [51] int. Cl. F28d 19/00 [58] Field of Search 165/8, 9, 10

[56] References Cited UNITED STATES PATENTS 3,401,741 9/1968 Paluszny et a1 165/8 3,586,096 6/1971 McLean 165/8 3,568,759 3/1971 Blech 165/8 3,688,835 9/1972 Yamaguchi et a1 165/8 Primary ExaminerAlbert W. Davis, Jr. Attorney-Thomas J. Greer, Jr. et a1.

[57] ABSTRACT A microcellular ceramic thermal regenerator disc, for use in a gas turbine engine, has a slot formed in its periphery between adjacent pairs of drive pins, each slot having both its ends terminating short of the two end faces of the disc.

5 Claims, 4 Drawing Figures sum 1 0F 2 PATENTED DEC 2 5 I975 SHEET 2 0F 2 THERMAL REGENERATORS The present invention relates to thermal regenerators or heat exchangers and particularly to rotary heat exchangers for gas turbine engines.

A known form of gas turbine engine for motor vehicles incorporates a rotary heat exchanger which comprises a disc of microcellular ceramic material. The disc is caused to rotate by driving means applied to solid semi-cylindrical ceramic pins cemented into axial grooves cut in the periphery of the microcellular matrix at intervals around its circumference.

Circular rubbing seals engage the end faces of the matrix and define a central area through which the compressed air to be introduced to the combustion chamber and the exhaust gas from the power turbine flow in opposite directions, being separated from each other by a diametral member across the seals.

Since the hot exhaust gas enters approximately one half of the face of the matrix whilst the heated compressed air leaves the remaining half of the same face, the whole of this face is at a high temperature relative to the opposite face through which the cold air enters and the cooled exhaust leaves the matrix. Theresultant temperature gradient between these two faces can be readily accommodated by the disc material.

The periphery of the disc is the portion outside that defined by the circular seals and consists of a hoop of microcellular matrix with the solid drive pins spaced at intervals around its circumference.

This periphery is usually immersed in high pressure, low temperature air and a sharp temperature gradient therefore exists on the hot face of the disc at the diameter defined by the seal. 1

Radial thermal cracks are initiated by this temperature gradient across the peripheral hoop of microcellular matrix at the narrow portions radially beneath the drive pins. The present invention is concerned with reducing the tendency for such cracks to occur or to control such cracking so as to minimise its adverse effects.

Attempts have already been made to deal with this problem. For example, in British Patent No. 1,202,840 (equivalent to US. Pat. No. 3,586,096 issued to Mc- Lean) a rotary ceramic regenerator, or heat exchanger, is disclosed which has diametrical slots formed in its periphery in order to relieve thermal stresses set up in the edge portion of the regenerator core or matrix. In that patent each of the slots has one of its ends terminating in an end face of the regenerator, i.e., the slot is openended, in an area where one of the said seals is in rubbing contact with the said face of the regenerator. Furthermore, the slots do not extend radially inwardly beyond the inner edge of the seal.

With this prior art arrangement it is advisable to fill at least the ends of the slots with a cement in order to reduce air leakage. We have found that if this prior art arrangement is employed, and the slots are filled with a cement in this way, the cement falls out during operation. This is because of the difficulty in obtaining a cement which has all the necessary characteristics to operate in the environment in question, and in particular has a coefficient of thermal expansion which is equal to that of the material from which the thermal regenerator matrix is made.

We have also found that in the prior art arrangement, where the depth of the slots does not extend below the seal, that there may still be areas of substantial thermal stress set up in the region of the base of the slots.

According to the present invention in a rotary heat exchanger, of the kind described, each of those portions of the hoop of microcellular matrix which are. between the driving pins has a slot formed or cut in it, each slot extending from the outer surface of the hoop radially inwardly and having both its ends terminating short of the two end faces of the matrix.

By this construction a wall of matrix material is left between each end of the slot and the rubbing seal so that the latter does not have to rub across an open end of the slot or across cement contained in that end.

According to a preferred aspect of the present invention each said slot terminates radially inwardly of said rubbing seal.

By this preferred arrangement it has been found that the adverse effects of thermal stresses are kept clear of the region of the matrix which is contacted by the rubbing seal and an undesirable break-up of the matrix caused by extensive cracking is prevented.

How the invention may be carried out will now be described, by way of example only, and with reference to the accompanying drawings in which:

FIG. 1 is a side elevational view of a rotary heat exchanger and associated seals;

FIG. 2 is a fragmentary view to a larger scale of part of FIG. 1;

FIG. 3 is a fragmentary sectional view taken on the line X-X in FIG. 2; and

FIG. 4 is a half-sectional view taken through the zone A of the heat exchanger of FIGS. 1 to 3, together with the drive arrangement.

A rotary heat exchanger for a gas turbine engine comprises a disc 1 made of ceramic material having a microcellular structure in which passages extend axially through the disc.

The disc carries a plurality of drive pins 3 set in grooves 4 in its outer periphery or hoop 2. The disc 1 can be rotated by driving the pins 3 by an arrangement which is shown in FIG. 4 and described later.

A circular sea] 9 is located on the hot side 5 of the disc and a second circular seal 10 on the cold side 6 of the disc. The seal 9 has a generally diametrical portion 9a which divides the hot side into two zones A and B, but does not pass through the centre of the disc 1.

All parts of the matrix move alternatively from the low pressure zone A in which they are subjected to exhaust gases from the turbine to the high pressure zone B in which they are subjected to compressed air which is fed to the combustion chamber of the engine. The purpose of the matrix is to transfer heat from the exhaust gases to the compressed air and thus preheat the latter.

The exhaust gasesimpinge on the surface 5 of the matrix, pass through-the-axial passages in the matrix centres of the surface and the periphery 2, in particular in the region marked R in FIG. 3.

Because of this temperature gradient there is a tendency for cracks to develop in the microcellular hoop 2 at its narrowest sections which are just below, i.e., radially inwardly of, the grooves 4 in which the pins 3 are located.

This is because, in those regions of the hoop 2 where the drive pins 3 are located there is the maximum loading caused by the superposition of mechanical stress applied through the drive pins, on the thermal stress which is already being applied to the hoop. This maximumloading is normally sufficient to cause cracking of the hoop in the up at these points.

In order to reduce the tendency for these cracks to occur, radial slots 11 are cut into the circumference of the microcellular hoop 2 midway between adjacent drive pins 3 commencing at a distance between 0.05 inch and 0.1 inch from the hot side 5 of the disc and extending axially approximately one third of the thickness of the disc. The depth of the slots 11 adjacent to the hot side is sufficient to penetrate into the flow area within the seal diameter, and is progressively reduced across the thickness of the disc, ie. at their deepest the slots extend radially inwardly of the seal.

Both ends of each slot 1 l terminate short of the two end faces, 5 and 6 of the matrix. In particular there is a thickness of matrix 7 between the end of the slot ,11 and the face 5 against which the seal 9 is in rubbing contact.

The slots 11 are filled with a ceramic filler material 8 to prevent leakage of the compressed air around the periphery into the flow area.

Thus by applying the present invention a weak section to the hoop 2 is provided remote from the drive pins 3. This in turn reduces the loads in the vicinity of the drive pins 3 and prevents or reduces the cracking which occurs in these regions.

The drive arrangement for the rotary heat exchanger will now be described with reference to FIG. 4, in which those parts of the heat exchanger which have almarked with the same reference numerals.

The disc 1 has a solid ceramic hub 12 and is rotatable about an axis Y-Y. A ring gear 13, having teeth 13a, is drivingly connected to the pins 3 by means of a plurality of blade springs 14, one spring being associated with each drive pin 3.

The teeth of the ring gear 13 mesh with a driving pinion (not shown) by which the ring gear 13 is driven, in

a manner similar to that shown in FIG. 1 of British Pat. No. 1,202,840.

The seals 9 and 10 are urged into contact with the hoop 2 of the regenerator by springs 15.

1. A rotatable thermal regenerator core for use in a gas turbine engine, including,

a. a disc of microcellular ceramic material;

b. a plurality of drive pins set in the periphery of the disc; the pins adapted to be engaged by an element for rotating the ceramic disc,

c. slots formed in the periphery of the disc, one between each adjacent pair of drive pins, the slots adapted to be filled with a ceramic filler material,

d. each slot having both its axially extending ends terminating short of the two faces of the disc.

2. The thermal regenerator core of claim 1 in which each slot is peripherally located mid-way between any two adjacent driving pins.

3. The thermal regenerator core of claim 1 in which each slot is of an axial extent equal to a third of the thickness of said ceramic disc.

4. The thermal regenerator core of claim 1 in which each slot is tapered in axial width, having its greatest width at the disc periphery and its least width radially inwardly from the disc periphery.

5. The thermal regenerator core of claim 4 including,

a. rubbing seals engaging circular zones on both sides of the ceramic disc near the disc periphery,

b. the said tapered slots having radially innermost portions which are radially inwardly of said rubbing seals.

2 3 3 UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No. 3,780,792 Dated December 25, 1973 Inventor) James Alexander Ritchie It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Assigneei British Leyland Truck and Bus Division Limited Leyland, Lancashire, England Claims priority of Great Britain 07991/71 March 25, 1971 Signed and sealed this 4th day of February 1975.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Arresting Officer Commissioner of Patents 

1. A rotatable thermal regenerator core for use in a gas turbine engine, including, a. a disc of microcellular ceramic material; b. a plurality of drive pins set in the periphery of the disc; the pins adapted to be engaged by an element for rotating the ceramic disc, c. slots formed in the periphery of the disc, one between each adjacent pair of drive pins, the slots adapted to be filled with a ceramic filler material, d. each slot having both its axially extending ends terminating short of the two faces of the disc.
 2. The thermal regenerator core of claim 1 in which each slot is peripherally located mid-way between any two adjacent driving pins.
 3. The thermal regenerator core of claim 1 in which each slot is of an axial extent equal to a third of the thickness of said ceramic disc.
 4. The thermal regenerator core of claim 1 in which each slot is tapered in axial width, having its greatest width at the disc periphery and its least width radially inwardly from the disc periphery.
 5. The thermal regenerator core of claim 4 including, a. rubbing seals engaging circular zones on both sides of the ceramic disc near the disc periphery, b. the said tapered slots having radially innermost portions which are radially inwardly of said rubbing seals. 